Method for cleaning, passivation and functionalization of si-ge semiconductor surfaces

ABSTRACT

A method for in-situ dry cleaning of a SiGe semiconductor surface, ex-situ degreases the Ge containing semiconductor surface and removes organic contaminants. The surface is then dosed with HF (aq) or NH 4 F (g) generated via NH 3 +NH or NF 3  with H 2  or H 2 O to remove oxygen containing contaminants. In-situ dosing of the SiGe surface with atomic H removes carbon containing contaminants.

PRIORITY CLAIM AND REFERENCE TO RELATED APPLICATION

The application is a divisional of and claims priority under 35 U.S.C. §120 and 121 from prior application Ser. No. 14/062,136, which was filedon Oct. 24, 2013 and claims priority under 35 U.S.C. § 119 from priorprovisional application Ser. No. 61/717,749, which was filed Oct. 24,2012.

FIELD

A field of the invention is semiconductor fabrication. Exampleapplications of the invention include processing of epitaxial Germanium(Ge) semiconductor surfaces, e.g., Ge containing wafers for atomic layerdeposition. The invention is particularly applicable to SiGe.

BACKGROUND

Existing cleaning methods of the germanium surface involve wet chemicaletching, ion bombardment, or very high temperature processing. Thelatter two processes are incompatible with commercial semiconductorlogic processing. The wet cleaning method is extremely difficult tointegrate into common process modules. The wet cleaning methods roughenthe Ge surface leaving a surface that is disordered and/or left withcontaminants, The disorder can be reduced by high temperature processing(875° C.), which is undesirable in commercial semiconductor processingbecause it induces dopant diffusion.

There are numerous previous reports of wet H₂O₂ cleaning and high dose Hcleaning of Si, SiGe, and Ge. The Ge alloys (SiGe and GeSb) areimportant since they will likely be employed in commercial devices priorto pure Ge for channels, sources, and drains. Anthony et al. describedthat cleaning of silicon surfaces by remote RF hydrogen plasma in mTorrrange after wet cleaning that can remove carbon and oxygen from theSi(100) surface. B, Anthony et al., “In situ Cleaning of SiliconSubstrate Surfaces by Remote Plasma-Excited Hydrogen”, J. Vac. Sci.Technol. B 7(4), (1989). A modification with wet cleaning and dosingwith a remote 1-1 plasma source at an optimized Si sample temperature of250° C. demonstrated both carbon and oxygen could be removed fromSi(100) to produce a flat surface and a sharp RHEED pattern. D. Kinoskyet al., “Hydrogen Plasma Cleaning of the Si(100) Surface: Removal ofOxygen and Carbon and The Etching of Si,” Materials Research Society'Proc 315, (1993). The need to avoid plasma damage is critical; Tae etal. developed a defect-free, in situ cleaning of wet cleaned siliconusing an ECR UHV hydrogen plasma treatment at a 560° C. surfacetemperature; however, to avoid ion damage a positive voltage had to beapplied to the sample. See, Tae, et al., “Low-Temperature in situCleaning of Silicon (100) Surface by Electron Cyclotron ResonanceHydrogen Plasma,” J. Vac. Sci. Technol. B 13, 908 (1995).

For SiGe, similar results have been reported. Li et al. employed ECRatomic H cleaning with 20 eV ion energy after wet cleaning with HCl:H₂O₂and HF to remove metallic and organic impurities from SiGe samples at250° C., but it is unclear if oxygen was removed. Li et al., “SiGe GateOxide Prepared at Low Temperatures in an Electron Cyclotron ResonancePlasma,” Appl. Phys. Lett. 63, 2938 (1993).

The worked described by Jones et al. is the only previous dry cleaningmethod known to the present inventors for a germanium containingsemiconductor device. That process employed UV ozone and an extremelyhigh temperature and long duration (>12 hr) anneal. See, D. E. Jones etal. “Scanning Tunneling Microscopy Study of Cleaning Procedures forSiGe(001) Surfaces,” Surf. Sci Vol. 341, No. 1, pp. 1005-1010 (1995).The completely gas phase process produced a 1-2 nm oxide layer, butrequired extensive annealing up to 1050° C. for oxide desorption whilemaintenance of doping profiles in semiconductor requires processingbelow 500 C.

Others have reported that atomic hydrogen can be an effective way toremove oxygen and possibly carbon contamination from the Si/SiGesurfaces during cleaning, and the H does serve as a cleaning mechanismagent. Either high atomic H cleaning doses or wet cleans were employed,both of which induce etching. Since there is a great interest in usingGe as channel material in FinFETs, any ex-situ acid wet cleaning or highatomic H dose procedure should be avoided to minimize etching andsurface roughness. Prabhakarana, et al., “An efficient Method forCleaning Ge(100) Surface,” Surface Science Volume 316, Issues 1-2, 1Sep. 1994, Pages L1031-L1033.

A known passivation method uses H₂O gas phase dosing to passivate andfunctionalize an already cleaned surface. See, J. S. Lee, et. al.,“Atomic Imaging of Nucleation of Trimethylaluminum on Clean and H2OFunctionalized Ge(100) surfaces,” Journal of Chemical Physics, 135,054705, (2011). Other gas phase passivation methods include nitridationand oxidation. Nitridation of the Ge surface is typically performedusing a plasma source to produce a thermally stable Ge oxynitride or Genitride layer in order to suppress the out-diffusion of GeO from the Gesurface into the high-k dielectric layer during the post-depositionannealing process, Oxidation using ozone or high pressure O₂ is alsofound to passivate the Ge surface by forming a stoichiometric GeO₂layer, which minimizes the suboxide species at the interface. However,to scale down the equivalent oxide thickness (EOT) of the Ge-channelMOSFET device, the thickness of these passivation layers has to bereduced to about one monolayer (ML).

Others have reported passivation methods on the SiGe(100) surfaceincluding growth of a Si passivation layer. These methods can result innon-uniform. growth unless very thick passivation layers are used. Yanget. al. reported on the passivation of the SiGe surface using an Al₂O₃layer but the Al₂O₃ layer was very thick (20 nm), which would be bad forscaling of the equivalent oxide thickness (EOT) in MOSFETs, wherepassivation layers more than 1 nm are not acceptable. See, Yang et al.,“Effective passivation of defects in Ge-rich SiGe-on-insulatorsubstrates by Al₂O₃ deposition and subsequent post-annealing,” SolidState Electronics, Volume 60, Issue 1, pp 128-133. The Al₂O₃ passivationresulted in SiO₂ film growth.

Thermal oxidation passivation methods of the SiGe surface lead topreferential oxidation of Si species. This produces Ge-rich layers nearthe SiGe-oxide interface, which is known to cause degradation of theoxide properties.

SUMMARY OF THE INVENTION

A preferred method for in-situ dry cleaning of a SiGe semiconductorsurface, ex-situ degreases the Ge containing semiconductor surface andremoves organic contaminants. The surface is then dosed with HF (aq) orNH₄F (g) generated via NH₃+NH or NF₃ with H₂ or H₂O to remove oxygencontaining contaminants. In-situ dosing of the SiGe surface with atomicH removes carbon containing contaminants.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1F illustrates a preferred embodiment method for in-situcleaning, passivation and functionalization of Ge containing surfaces;

FIG. 2 is an image of an experimental N-type Ge(100) surface treatedwith high concentration H₂O₂ vapor at a sample temperature of 300° C.followed by a subsequent anneal at 750° C.;

FIG. 3A is a filled state STM image of an experimental H₂O₂-dosedGe(100) surface at RT (room temperature) showing that 0.95 ML(monolayer) of a Ge surface is covered by H₂O₂ chemisorption; FIG. 3B isa plot showing conductance measurements obtained with STS (scanningtunneling spectroscopy) taken on various surface sites of the image ofFIG. 3A;

FIG. 4A is a filled state STM image of an experimental H₂O₂-dosedGe(100) surface at RT annealed to 100° C. showing change in surfacebonding configuration; FIG. 4B is a plot showing conductance STSmeasurements taken on the annealed surface of FIG. 4A, which shows shiftin Fermi level (0V sample bias);

FIG. 5A is a filled state STM image of an experimental TMA/H₂O₂/Ge(100)surface dosed at RT annealed to 200° C. showing ordered structureformation (vertical rows); FIG. 5B is a plot showing conductance STSmeasurements taken on the experimental TMA/H₂O₂/Ge(100) surface annealedto 200° C. compared to clean Ge surface;

FIG. 6A is a filled state STM image of an experimental H₂O₂-dosedSiGe(100) surface at RT showing the SiGe(100) surface covered by H₂O₂chemisorption; FIG. 6B is a plot showing STS taken on various surfacesites of the clean SiGe surface and the H₂O₂/SiGe surface;

FIG. 7A is a filled state STM image of an experimental H₂O₂-dosedSiGe(100) surface at RT annealed to 290° C. showing change in surfacebonding configuration; FIG. 7B is a plot showing conductance SISmeasurements taken from the annealed surface showing shift in Fermilevel (0V sample bias);

FIG. 8A is a filled state STM image of an experimentalTMA/H₂O₂/SiGe(100) surface dosed at RT annealed to 240° C. showingordered structure formation (vertical rows); FIG. 8B is a plot showingconductance STS taken on the TMA/H₂O₂/SiGe(100) surface annealed to 310°C. and compared to clean SiGe and H₂O₂/SiGe surfaces;

FIG. 9 is a plot of data showing results comparing multi-dose andextended single dose high concentration 4-5% H₂O₂ (g) in-situ drycleaning and subsequent annealing; and

FIGS. 10 and 11 are plots that shows XPS results from preferredembodiment ex-situ wet HF cleaned SiGe(100) samples (column I) and thesample after carbon is cleaned from the SiGe surfaces (column II).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the invention is method for in-situ dry cleaning of aSiGe semiconductor surface doses the SiGe surface with ex-situ wet HF ina clean ambient environment or in-situ dosing with gaseous NH₄F toremove oxygen containing contaminants. Dosing the SiGe surface withatomic H removes carbon containing contaminants. Low temperatureannealing pulls the surface flat. Passivating the SiGe semiconductorsurface with H₂O₂ vapor for a sufficient time and concentration forms ana oxygen monolayer(s) of —OH sites on the SiGe. Second annealing theSiGe semiconductor surface is conducted at a temperature below thatwhich would induce dopant diffusion.

An embodiment of the invention is a method for in-situ dry cleaning of aSiGe semiconductor surface, ex-situ degreases the Ge containingsemiconductor surface and removes organic contaminants. The surface isthen dosed with HF (aq) or NH₄F (g) generated via NH₃+NH or NF₃ with H₂or H₂O to remove oxygen containing contaminants. In-situ dosing of theSiGe surface with atomic H removes carbon containing contaminants.

An embodiment of the invention is a method for cleaning epitaxial Gecontaining semiconductor surfaces. The method is generally applicable togermanium containing semiconductors including Ge and GeSn, but excludingSiGe. Ge containing semiconductor wafer can be more challenging to cleanthan Si since carbon segregates to the surface of Ge containing wafer.The method uses high concentration H₂O₂ vapor in a non-disruptiveprocess to clean wafers in a completely in-situ manner. By exposing anuntreated wafer to high concentration H₂O₂ (g), followed by ahigh-temperature anneal, the method cleans the Ge semiconductor waferleaving an ordered and flat surface. An anneal in the present inventionis preferably 550° C. or below and can be, for example, only at 500° C.,and with atomic H can reduced to ˜200° C. The method produces a clean,ordered, flat Ge containing semiconductor surface (excluding SiGe) readyfor atomic layer deposition and CMOS processing. In preferredembodiments, a Ge containing wafer is first degreased and treated withan organic solvent, e.g., acetone, methanol; the wafer is placed in thevacuum chamber, and is treated with H₂O₂ vapor, preferably in a highconcentration (e.g., 4-5% H₂O₂ (g) in H₂O (g)). Annealing is thenconducted at a temperature less than a temperature that would inducedopant diffusion, e.g., 550° C. or less, and preferably about 250° C.Temperatures for source or drain material application annealing arepreferably no more than ˜550° C., while temperatures for channelmaterial application are preferably no more than ˜350° C.

Present methods demonstrate improvement over the only method known tothe inventors to achieve high density monolayerpassivation/functionalization of a Ge surface. While the belief is notdispositive or necessary to distinguish the present invention from theart, it is believed that the method is the first demonstration of theeffect of H₂O₂ (g) functionalization on nucleation of TMA(trimethylaluminum) on the Ge surface. The present methods provideatomically ordered Ge surfaces without requiring ex-situ acid cleaningprocedures or in-situ ion sputtering treatments.

This invention also provides monolayer functionalization, passivation,and nucleation of gate oxide and tunneling oxides on Ge and SiGesurfaces for atomic layer deposition (ALD) of dielectrics.

The cleaning can be employed either for deposition of gate oxide or forcleaning the source and drains. The cleaning procedure includes: dosingwith high concentration gas phase H₂O₂ to remove carbon and annealing orthermal atomic H exposure to remove the oxide formed by the H₂O₂ (g).The invention provides an all dry moderate temperature ˜550° C. or lessprocess for cleaning Ge wafers.

When forming a source/drain material, preferred embodiments limit theannealing temperature to a maximum of ˜550° C. For formation of channelmaterial, in preferred embodiments the annealing limit is a maximum of˜350° C. with atomic hydrogen use during the annealing to assist in theoxide removal. A temperature range during annealing with atomic hydrogenis in the range of ˜200° C.-350° C. After H₂O₂ (g) dosing and annealing,the clean surface is ready for passivation, functionalization, andnucleation of atomic layer deposition. After low concentration H₂O₂ (g)dosing, the annealing should be held to below 100° C. and then after.TMA dosing onto the H₂O₂ dosed surface, annealing is preferablyconducted between 200-300° C.

In a preferred embodiment, ex-situ wet dipping in HF followed by in-situatomic H dosing is used to effectively clean SiGe wafers if the surfaceis kept in an inert atmosphere between the ex-situ wet treatment andin-situ atomic H treatment. The ex-situ HF clean will effectively removeall oxygen containing contaminants from the surface while the in-situatomic H treatment will effectively remove all carbon containingcontaminants. Another preferred embodiment provides a method for acompletely in-situ treatment and uses NH₄F to effectively clean SiGewafers. In-situ dosing of NH₄F will effectively remove carbon and oxygencontaining species (SiOx and GeOx) from the surface. The NH₄F can bedosed via in-situ formation via NF₃+atomic H, thermally mixing NH₃+NF₃,or plasma mixing of NF₃ with H₂ or H₂O.

Dielectric deposition is required for gate oxides but can also be usedin methods of the invention for unpinning the contacts to sources anddrains on Ge and Ge alloy based devices. For example, for gate oxides,in order to scale the equivalent oxide thickness (EOT) of a Ge(100) CMOSwhile maintaining a high mobility, a monolayer passivation andnucleation layer is needed whose formation does not disrupt thesubstrate. An example preferred monolayer passivation and nucleationscheme is saturation of Ge(100) with a monolayer of H₂O₂ at 300K,followed by a 100° C. anneal to form a layer with a high density ofGe—OH bonds, followed by saturation with TMA at 300K, and followed by a200° C. anneal, which can readily be performed in an ALD (atomic layerdeposition) reactor. A similar procedure can be used for oxidedeposition on the source and drain. The procedure can be used for othercrystal faces including SiGe(110) which has slightly different bonding.Saturation of Ge(100) with a monolayer of H₂O₂ chemisorbates at 300Kforms a high density of Ge—OH bonds. This is followed by a 100° C.anneal which electrically unpins the surface. Subsequently, a saturationdose of TMA on the H₂O₂/Ge surface at 25 C followed by a 200-300 Canneal forms a monolayer of thermally stable Al—O bonds. This canreadily be performed in an ALD (atomic layer deposition) reactor. Theprocedure can also be used for other Ge containing semiconductors,including SiGe and GeSn. The procedure can also be used for othercrystal faces including SiGe(110) and Ge(110). The SiGe(110) surface hasimportance in MOSFET development as new geometries are considered forthese devices.

A preferred method for in-situ dry cleaning of a Ge containingsemiconductor surface includes ex-situ degreasing of the semiconductorsurface to remove of organic contaminants. In-situ, using highconcentration H₂O₂ gas phase precursor, multiple monolayers of GeO_(x)are formed to remove carbon contamination. In-situ, GeO_(x) is removedby annealing at a moderate temperature to remove the oxide and leave anatomically flat surface. The moderate temperature is below the levelthat would induce dopant diffusion. Preferably, the high concentrationgas phase precursors are 4-5% H₂O₂ (g) in H₂O (g), and the annealingcomprises annealing at ˜550° C. or less for source and drain materialapplication and below 350° C. with atomic H for channel materialapplication.

Preferred embodiments of the invention will now be discussed withrespect to the drawings. The drawings may include schematicrepresentations, which will be understood by artisans in view of thegeneral knowledge in the art and the description that follows. Featuresmay be exaggerated in the drawings for emphasis, and features may not beto scale.

FIGS. 1A-1F illustrate a preferred method of the invention. The methodis performed completely in-situ, and anneal temperatures are low enoughto be conducted in standard semiconductor processing. In FIG. 1A, asubstrate containing Ge is provided. The substrate can be, for example,a Ge(100) crystal. The method is applicable to other semiconductors,such as SiGe and GeSn, and also other crystal faces including Ge(110)and SiGe(110), but for Si containing semiconductors an in-situ dry NH₄For ex-situ wet HF in a clean atmosphere cleaning step must be included.A Ge containing substrate 10 will have organic contamination 12 andcarbon contamination 14. Organic contamination 14 is removed in FIG. 1B,such as with a wet solvent and then the substrate 10 is placed vacuum inFIG. 1C. The organic cleaning in FIG. 1B is an organic ex-situ solventcleaning that is used to remove organic contamination 12 from thesurface prior to any in-situ treatment. A dry cleaning process isconducted in FIG. 1D. The dry cleaning process uses H₂O₂ or H to removethe carbon contamination 14 and leave a clean GeO_(x) surface 16. In anexample preferred process, hydrogen peroxide gas, H₂O₂ (g), is used toremove hydrocarbon contamination. By using H₂O₂ in the gas phase,extensive etching of the surface can be avoided. Annealing is conductedin FIG. 1E to remove GeOx and this produces a clean semiconductorsurface 18 that is ready for further processing/device fabrication inFIG. 1F. Advantageously, an anneal can be performed in a moderatetemperature range, below 550° C., which avoids the very hightemperature, e.g., 875° C., processing for methods that include many wetcleaning processes for Ge semiconductor services. In a preferredembodiment, an anneal is conducted at only ˜500° C. after H₂O₂ (g)dosing, and this successfully removes oxide and carbon and can be usedto form source and drain materials. The anneal temperature is reduced tobelow ˜350° C. with use of atomic IT Use of atomic H during the annealcan drastically reduce the anneal temperature to preferably ˜200-300°C., for example. The surface in FIG. 1F is functionalized and passivatedvia low concentration H₂O₂. It is reactive to ALD and has a monolayerwith a Fermi level that is unpinned after a 100° C. anneal. The surfaceis left with terminated with at least oxygen species (—OH or —O) persurface atom, which doubles the number of potential reactive sitescompared to conventional passivation and ALD functionalization methods(H₂O gas dosing).

Experiments have shown that when the H₂O₂ (g) dosed surface is initiallyannealed to 100° C., the bonding configuration on the surface changesresulting in unpinned Fermi level. After dosing with TMA, an anneal of˜200-300° C. is conducted. . The H₂O₂ (g) functionalized surface isstable at 100° C. after H₂O₂ (g) dosing and 300° C. after TMA dosing onH₂O₂/Ge surface. A combination of complete monolayer H₂O₂functionalization followed by TMA reaction provides a thermally stableAl—O bond, which provides a high density nucleation template for furtherhigh-k oxide deposition.

Experiments

Experiments were carried out in a UHV chamber with a base pressure of2×10⁻¹⁰ Torr. N-type Ge(100) samples were sonicated three times in highpurity acetone, methanol and high performance liquid chromatography(HPLC) water to degrease the samples. Subsequently, the samples wereblown dry with N₂ (g). After loading into the UHV chamber, samples wereinitially degassed by heating to 400° C. Afterwards, the samples weretransferred to the ALD chamber with a base pressure of 2×10⁻⁸ Torr.Samples were subsequently dosed with H₂O₂ (g) while the sampletemperature was maintained at 300° C. Two different H₂O₂ (g) sourceswere used in experiments; a high concentration (4-5% H₂O₂ (g) in H₂O(g)) H₂O₂ vapor source from RASIRC® and a commercially available lowconcentration H₂O₂(2% H₂O₂ (g) in H₂O (g)). The high and lowconcentration gas sources still were both prepared from a 30% H₂O/H₂O(liquid) solution. A vapor of this liquid solution which only has ˜2%H₂O₂ (g)/H₂O (g) served as the low concentration vapor source and ahigher concentration ˜4-5% vapor served as the high concentration sourcewhen dosing.

All dosing lines and valves were made from Teflon. After dosing withH₂O₂ samples were transferred to the TAW chamber for structural andchemical analysis. An anneal was employed to remove the oxide layer (butat relatively moderate temperatures compared to most wet processingtechniques) and obtain large terraces on the surface. X-rayphotoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM)were used to analyze the chemical and structural configuration of thesurface of Ge samples. In a separate experiment, Auger electronspectroscopy (AES) was used to quantify the amount of oxygen and carbonon the surface after treating the samples with thermal atomic hydrogen.Atomic hydrogen was produced using an Oxford Applied Research® TC50thermal gas cracker. Atomic hydrogen was dosed at a pressure of 10⁻⁶Torr.

Experiments showed that by using a high concentration (4-5%) gas phaseH₂O₂ source, carbon contamination can be removed from Ge(100) withoutwet pretreatment. Gas phase H₂O₂ leaves a multilayer GeOx which can bedesorbed from the surface by annealing. The H₂ ₂ (g) forms about 4 ML ofGeOx which readily desorbs from the surface at elevated temperatureleaving an atomically ordered and clean surface.

A Ge(100) surface was dosed with 60 MegaLangmuir of high concentrationH₂O₂ (g) at a sample temperature of 300 C. The high concentration H₂O₂source is built by RASIRC® and delivers a high ratio (4-5%) of vaporH₂O₂/H₂O. The source temperature is 10° C. while dosing. After formingmultilayer GeO_(x) on the Ge(100) surface, an anneal between 500-750° C.(the higher temperature was used in experiments to provide for betterSTM images) for 20 minutes removes the oxide layer leaving an ordered,flat, and contaminant free Ge surface as shown in FIG. 2. Bright whitespots are in FIG. 2 are Ge adatoms.

Once a clean Ge surface is achieved, a saturation dose of lowconcentration H₂O₂ (g) is performed at below 100° C. to give a fullmonolayer of —OH sites which terminates Ge dangling bonds. Thesaturation dose is self limiting, because no more adsorption occurs atsaturation. The saturation dose provides the highest coverage that canbe achieved. This passivation reduces the electronic density of statesin the Ge band gap that occur when under coordinated Ge atoms exist onthe surface. A Ge(100) surface dosed with 2.25×10⁶ L of H₂O₂ (g) at 300Kis shown in FIG. 3A. Nearly 100% of the surface is covered with H₂O₂dissociative chemisorptions sites, with only a very few dangling bondsleft unreacted. These few dangling bonds are circled. The density ofstates measured from these surface sites are compared in FIG. 3B. Thedata show that dangling bond sites have energy states near 0.5 eV,consistent with the presence of dangling bonds. The energy states around0.5 eV on the H₂O₂ sites are significantly reduced, showing that thedangling bond states are passivated by the —Oh bonds.

When the Ge—OH surface is annealed to 100° C., the surface bondingconfiguration changes as shown in FIG. 4A. It is likely the initial dosecould be at 100° C. instead of 25° C. also. The low temperature annealreduces the large surface dipole, unpinning the surface and leaving anelectronic structure similar to that of the clean surface. This shift inFermi level is shown in FIG. 4B, which shows the density of statesbefore and after the 100° C. anneal.

On the H₂O₂ (g) dosed Ge surface, a saturation dose of TMA is performedat 300K. TMA dissociatively chemisorbs to the oxygen on the surfaceGe—OH forming Ge—O—Al bonds, while hydrogen atoms promotes a —CH₃ TMAligand to desorb as CH₄. This leaves dimethylaluminum (DMA) andmonomethyl aluminum (MMA) bonded to the surface via an Al—O bond. Afterthe surface is annealed to 200° C., more methyl ligands desorb front thesurface and an ordered structure forms on the surface as shown by thevertical rows that are apparent in FIG. 5A. The result is a nearmonolayer of ordered non-stoichiometric alumina that forms on thesurface. TMA can also be dosed on the 100° C. annealed H₂O₂ dosed Gesurface. TMA will bond to the surface via a similar mechanism, and XPSdata confirms that the nucleation density of TMA is equal on both the25° C. as-dosed H₂O₂/Ge(100) surface and the 100° C. annealedH₂O₂/Ge(100) surface. Both result with an O to Al ratio of 1. FIG. 5Bshows the density of states of the TMA/100° C. annealed H₂O₂ (g)/Gesurface demonstrating a slightly large bandgap than the clean surfaceand with no states in the bandgap. This demonstrates an excellentinterface and template for further high-k oxide deposition because aftera single monolayer of DMA or MMA is on the surface, a very high kdielectric can be deposited by ALD as shown by R, Suzuki. See, Suzuki etal. “1-nm-capacitance-equivalent-thickness HfO2/Al2O3/InGaAsmetal-oxide-semiconductor structure with low interface trap density andlow gate leakage current density” in Applied Physics Letters, 100,132906 (2012).

The processing steps previously described for passivating andfunctionalizing the Ge(100) surface are very similar to the treatmentneeded to functionalize and passivate the SiGe(100) but note anadditional NH₄F cleaning step is required,

Once a clean SiGe(100) surface is achieved, a saturation dose of H₂O₂(g) is performed at 300K to give a full monolayer of —OH sites whichterminate SiGe dangling bonds. This passivation reduces the electronicdensity of states in the SiGe band gap caused by dangling bonds. TheSiGe(100) surface dosed with 2×10⁴ L of H₂O₂ (g) at 300K is shown inFIG. 6A. The density of states measured from this surface is shown andcompared to the clean SiGe(100) surface in FIG. 6B. As expected, H₂O₂(g) dosing (red curve) pins the Fermi level near the valence band edgedue to the large surface dipole. The H₂O₂ (g) dosing also eliminateselectronic states in the bandgap caused by dangling bonds on undercoordinated atoms on the surface, which demonstrates successfulpassivation of the surface.

When the SiGe—OH surface is annealed to 290° C., the surface bondingconfiguration changes, as shown in FIG. 7A. The large surface dipole isreduced, unpinning the surface and leaving an electronic structuresimilar to that of the clean surface. This shift in Fermi level is shownin FIG. 7B, which shows the density of states before and after the 290°C. anneal. The surface bonding configuration begins to change from theSiGe—OH surface at ˜180° C., and anneals between 200-300° C. arepreferred to provide the surface configuration change and reduce thesurface dipole.

On the H₂O₂ (g) dosed SiGe surface, a saturation dose of TMA (1×10⁵Langmuir) is performed at 300K. TMA dissociatively chemisorbs to theoxygen on the surface, while hydrogen atoms promotes a —CH₃ TMA ligandto desorb as CH₄. This leaves dimethylaluminum (DMA) bonded to thesurface via an Al—O bond. After the surface is annealed to 200-300° C.,more methyl ligands desorb from the surface and an ordered structureforms on the surface as shown by the vertical rows in FIG. 8A. Theresult is a near monolayer of ordered non-stoichiometric alumina whichforms on the surface. TMA can also be dosed on the 290° C. annealed H₂O₂(g) dosed SiGe surface. TMA will bond to the surface via, a similarmechanism as previously described. FIG. 8B shows the density of statesof the TMA/H₂O₂/SiGe surface, which demonstrates a slightly largebandgap than the clean surface and with no states in the bandgap and anunpinned interface. Once the monolayer of TMA bonds to the surface, veryhigh-k dielectrics such as HfO₂ can readily be deposited since they bondto Al—OH functional groups. This demonstrates a high quality interfaceand template for further high-k oxide deposition.

The SiGe(100) experiments provide strong evidence that the present ALDnucleation methods will work on the SiGe(110) surface. Others have shownthat WO functionalization of the Si(110) surface takes place in adissociative manner, which was demonstrated on the Si/SiGe/Ge(100)surface. While not bound by the theory, we believe that a similardissociative chemisorption occurs on the SiGe(110) surface when dosedwith either H₂O (g) or H₂O₂ (g) indicating that the presentfunctionalization with H₂O₂ should work well on the SiGe(110) or Ge(110)surface.

Experiments also tested different dosing conditions of air exposedGe(100) samples at 300K with low concentration H₂O₂ (g). For dosing with20 mTorr 2% H₂O₂ (g), by increasing the dosing time from 30 seconds(6×10⁵ L) to 45 seconds (9×10⁵ L), the concentration of surface oxygenhas been increased to 1.5 monolayers. While increasing the dosing timeof the 2% H₂O₂ (g) increased the oxide thickness, it was still too smallto remove all the carbon after annealing so the 4-5% H₂O₂ (g) wasdemonstrated to be much more effective. Experiments showed that bydosing a Ge(100) sample at 300K for 30 seconds (1.65×10⁷ L) with 550mTorr 4-5% H₂O₂ (g), the oxygen level increased 4 fold compared to the2% H₂O₂ (g) dosed surfaces, indicating successful formation ofmultilayers of oxide on the Ge(100) surface.

Experiments showed that a multilayer of the oxide formed via the 4-5%H₂O₂ (g) 1.65×10⁷ L dose at a surface temperature of 300K can be removedby annealing resulting in an atomically flat surface. Surface dosing at300K with 4-5% H₂O₂ (g) (1.65×10⁷ L) for 30 seconds and subsequentannealing at 700° C. for 30 minutes produced large terraces suitable forSTM imaging, but the oxide desorption is fast as demonstrated by a brief(˜60 sec) 3×10⁻⁹ Torr pressure rise upon heating to sample to 700° C.Levels of carbon contamination from image analysis in some samples wereless than 5%. Using larger doses of 4-5% H₂O₂ (g), carbon contaminationwas completely eliminated and this is verified by X-ray PhotoelectronSpectroscopy. The invention thus provides atomically ordered Ge surfaceswithout ex-situ acid cleaning procedures or in-situ ion sputteringtreatment. Contamination is reduced without any extensive ex-situ wettreatment of the surface. The process should work on all Gereconstruction since the process only depends on local bondingproperties

Multi dose and single dose cleanings were also tested, and the resultsare shown in FIG. 9. An air exposed sample was degassed in the UHVchamber at 400° C. removing the native oxide (columns I and II).Subsequently, the sample was dosed with 4-5% H₂O₂ (g) for 20 seconds at300° C. thereby reducing the carbon and growing a multi-layernon-stoichiometric germanium oxide (column III). Subsequent annealing at750° C. removes the oxygen from the surface (column IV). The same samplewas redosed for the second time with 4-5%. H₂O₂ (g) for 20 seconds at300° C. and subsequently annealed for 20 min at 650° C. The carboncontent reduced to half compare to previous step. (column V). An orderof magnitude higher dose (1.65×10⁸ L) and subsequent anneal at 500° C.(the experiment used 700° C. for the purpose of obtaining better STMimages) for 20 min completely removed the carbon from the surface(column VI).

To further understand the chemistry of carbon and oxygen removal from Geat elevated temperature (300° C.), the progression of carbon and oxygenlevels from its surface were analyzed with XPS, and the data are shownin FIG. 9. The XPS data has been normalized to the Ge 2p peak. Thesample was first treated with acetone, methanol and HPLC water. Watertreatment of the Ge surface forms a thick layer of oxide on top of thesurface resulting in a very large XPS oxygen peak. The initial carboncontent on the surface is ˜50% (column I). Degassing at 400° C. in UHVinduced all of the oxide layer to desorb along with half the carboncontent leaving about 25% carbon on the Ge(100) surface (column II).This reduction in carbon content is consistent with the desorption ofatmospheric hydrocarbon species which adsorbed on the oxide layer priorto loading the sample into the UHV chamber.

Degassed samples were transferred to the ALD chamber and dosed at 300°C. with 4-5% H₂O₂ (g) for a 20 second dose at 550 mTorr (1.1×10⁷ L)while maintaining sample temperature at 300° C. This produced arelatively thin oxide layer (3-10 monolayers) on the Ge surface andreduced the carbon content to about 15% (column III). A subsequentmoderate temperature anneal at 750° C. desorbed all the oxygen (columnIV) and pulled the surface flat. After the 750° C. anneal, bright whitefeatures were seen on STM images, which are consistent with carboncontamination due to the height of the features (5 Å) being inconsistentwith Ge adatoms which have a height of 2 Å; XPS data was also consistentwith carbon. It is expected that thermal anneal temperatures as low as500° C. would be sufficient or 250° C. with atomic H.

The sample was redosed at 300° C. with 4-5% H₂O₂ (g) for 20 seconds at560 mTorr (1.1×10⁷ L) and subsequently annealed at 650° C. It isexpected that thermal anneal temperatures as low as 500° C. would besufficient or 250° C. with atomic H. XPS data indicated that the secondH₂O₂ dose reduced the carbon contamination of the surface to about 7%(column V). This proves that by cycling samples through H₂O₂ (g) dosesand subsequent anneals, the carbon contamination can be systematicallyreduced. STM images showed lower densities of white features indicatinglower surface concentration of carbon than after a first H₂O₂ (g) doseand anneal cycle. Surfaces annealed to 650° C. and lower compared to750° C. were still flat and free of adatoms. It is expected that thermalanneal temperatures as low as 550° C. would be sufficient or 250° C.with atomic H. The number of cycles and cycling time is not important.Instead, it is the amount of vapor which is exposed to the surface. 1Langmuir=10⁻⁶ torr for 1 sec. The experiments have shown that 6×10⁷Langmuirs will clean the surface of carbon contamination. This can beprovided as one single dose or can be delivered over multiple pulses tothe same effect.

Experiments also showed that the cyclic dose/anneal process could bereplaced with a single long H₂O₂ (g) dose to achieved very low levels ofcontamination. A 5 min 4-5% H₂O₂ (g) dose at 550 mTorr (165×0⁶ L) at asample temperature at 300° C. and a subsequent anneal at 700° C. (orless) for 30 minutes is sufficient to completely remove the carbon fromthe surface (column VI). XPS data confirmed that such a long dosing time(165×10⁶ L) of 4-5% H₂O₂ (g) and subsequent anneal can completely removethe carbon from the surface. It is expected that thermal annealtemperatures as low as 500° C. would be sufficient or 250° C. withatomic H.

Experiments showed that a high concentration (30% H₂O₂/H₂O (l)) 4-5% gasphase H₂O₂ source, carbon contamination can be removed from Ge(100)without wet pretreatment. Gas phase H₂O₂ leaves a multilayer GeO_(x)which can be desorbed from the surface by annealing. The H₂O₂ (g) formsabout 4 ML of GeO_(x) which readily desorb from the surface at elevatedtemperature leaving an atomic ordered and clean surface.

Experiments showed that an air exposed SiGe(100) wafer can be cleaned byusing an ex-situ 2% HF/H₂O dip for 2 minutes followed by in-situexposure to 2400 L of atomic H can provide a nearly contaminant freesample. A wide concentration range of HF/H₂O will work. FIG. 10 showsthe XPS results from an ex-situ HF cleaned SiGe(100) sample (column I).After the sample is exposed to 2400 L of atomic H, the carboncontamination on the sample is reduced to 3% demonstrating that atomic Hcan efficiently remove carbon from the SiGe surface (column II). Theresidual oxygen contaminants on the surface are due to oxygen adsorptionbetween the ex-situ HF treatment and loading the sample into vacuum. Ifthe transfer is done in an inert environment, or if in-situ NH4F+atomicH treatment is done in-situ, there should be no residual oxygen on thesurface leaving a surface clean for ALD.

Another experiment demonstrated that maintaining the SiGe surface as ifit were in an inert atmosphere could also be accomplished by leaving HFliquid on the surface. Specifically, instead of transfer in inertatmosphere, this was done by leaving liquid 2% HF in H₂O on the SiGesurface until vacuum pumpdown began. The result of this cleaning methodis to give a surface which is completely oxygen free. This is thenfollowed by an in-situ 330 C atomic H treatment which removes the carboncontamination from the sample leaving a completely contaminant freesample. The results are shown in FIG. 11.

While specific embodiments of the present invention have been shown anddescribed, it should be understood that other modifications,substitutions and alternatives are apparent to one of ordinary skill inthe art. Such modifications, substitutions and alternatives can be madewithout departing from the spirit and scope of the invention, whichshould be determined from the appended claims.

Various features of the invention are set forth in the appended claims.

1. A method for in-situ dry cleaning of a SiGe semiconductor surface,comprising: ex-situ, degreasing the Ge containing semiconductor surface;ex-situ, removing organic contaminants; dosing the SiGe surface with HF(aq) or NH₄F (g) generated via NH₃+NH or NF₃ with H₂ or H₂O; in-situdosing the SiGe surface with atomic H to remove carbon contamination. 2.The method of claim 1, further comprising in-situ passivating with H₂O₂(g).
 3. The method of claim 2, further comprising in-situ nucleatingwith trimethylaluminum (TMA).
 4. The method of claim 3, furthercomprising second annealing at ˜200-300° C. is conducted after saidnucleating.
 5. The method of claim 1, wherein said dosing the SiGesurface with and comprises in-situ formation via NF₃+atomic H.
 6. Themethod of claim 1, wherein said dosing the SiGe surface with NH₄Fcomprises in-situ thermally or plasma mixing NH₃+NF₃. The method ofclaim 1, wherein said dosing the SiGe surface with NH4F comprisesin-situ plasma mixing of NF₃ with H₂ or H₂O.
 8. The method of claim 1,wherein said dosing the SiGe surface with HF comprises wet-dipping inHF/H₂O, followed by keeping the SiGe surface in an inert atmosphere andthen followed by said dosing the SiGe surface with atomic H, conductedin-situ.